Removable Control Line Barrier

ABSTRACT

A hydraulically operated downhole tool located at a depth where control line hydrostatic pressure would normally set the tool is temporarily isolated from hydrostatic pressure and changes thereto from well exposure or downhole operations until properly located. A removable barrier is placed in the control line to the tool at a height from the tool that limits the hydrostatic force exposed to the actuation mechanism for the tool. The preferred barrier is a rupture disc that is selectively broken with applied pressure from a remote location, typically the surface above the well. The mounting depth of the barrier can be varied to control the maximum hydrostatic pressure seen by the tool as it is advanced to the intended position.

FIELD OF THE INVENTION

The field of the invention is deep set tools operated with a control line from a surface and more particularly prevention of premature tool operation from control line hydrostatic at the desired mounting location.

BACKGROUND OF THE INVENTION

Downhole tools mounted to a string are operated remotely in several ways. A common way to actuate such tools is to run a small line outside the string to the tool and when tool operation is required pressure is added to the control line to operate the tool. As setting depth increases the amount of control line hydrostatic pressure increases. In very deep wells that can be over 3000 meters the control line hydrostatic pressure can exceed the setting pressure needed to actuate the downhole tool in question. This means that as the string is running the tool to the desired depth the tool can be triggered to operate at the wrong time.

In some applications an existing bottom hole assembly is tagged into by an upper completion through a connector referred to as a wet connect. In essence the lower portion of the wet connect is attached to the string and has an associated control line or lines that are closed off near the wet connect and extend further into the hole to the tool to be operated. The top portion of the wet connect stabs into the bottom portion to connect the string components together and to connect control line components together. As the connection is made up a valve opens in the tubing thus reducing the tubing pressure and potentially increasing the control line differential pressure on the downhole tool to further increase the risk of untimely operation.

To address this issue the control system for the downhole tool will have a removable barrier that limits the amount of hydrostatic pressure seen at the tool to the height of the control line fluid column that is below the barrier. When the tool is ready to be actuated the barrier can be removed with applied surface pressure or other techniques to then allow the full hydrostatic pressure and any further surface applied pressure to operate the tool when needed. One such removable barrier can be a rupture disc or a remotely actuated valve.

Rupture discs have been used in control lines in the past to isolate one redundant control line system from another until such time as the primary control line system developed a malfunction. These systems used a rupture disc to isolate the redundant systems from each other. Some systems like this are seen in U.S. Pat. No. 7,591,317; U.S. Pat. No. 7,637,324 and U.S. Pat. No. 7,762,335. In other applications a rupture disc is put into a control line to allow some equipment to be operated while isolating other equipment from control line pressure until a later time during which the barrier is then removed. An example of such systems is U.S. Pat. No. 6,349,770 (item 31). Other installations use a rupture disc as a backup entry passage to an existing control system as shown in U.S. Pat. No. 7,562,712. Other designs place explosively broken rupture discs near each tool to allow selective opening for access in a predetermined order.

Ultra-deep completions are a fairly recent phenomenon and bring about situations of high hydrostatic pressure that may prematurely or inadvertently set off hydraulically controlled tools. The present invention uses breakable barriers strategically located to limit hydrostatic pressure seen by the tool to be operated until proper placement is assured. The operation and placement of the removable barriers address fluctuations caused by well thermal conditions or pressure spikes occurring when mating connections downhole as described above. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawing while understanding that the full scope of the invention is to be determined by the appended claims.

SUMMARY OF THE INVENTION

A hydraulically operated downhole tool located at a depth where control line hydrostatic pressure would normally set the tool is temporarily isolated from hydrostatic pressure and changes thereto from well exposure or downhole operations until properly located. A removable barrier is placed in the control line to the tool at a height from the tool that limits the hydrostatic force exposed to the actuation mechanism for the tool. The preferred barrier is a rupture disc that is selectively broken with applied pressure from a remote location, typically the surface above the well. The mounting depth of the barrier can be varied to control the maximum hydrostatic pressure seen by the tool as it is advanced to the intended position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art system showing a control line going to a deep set tool where hydrostatic pressure can build to a high enough level to set the tool before the desired depth is reached;

FIG. 2 shows the placement of the removable isolation device in the control line to limit hydrostatic pressure at the tool until it is properly positioned to avoid premature actuation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a tubular string 10 with a hydraulically operated tool 12 located in a deep borehole 14. A control line 16 extends from a surface location 18 and is connected to the tool 12 which typically has a hydraulically responsive actuator of a type well known in the art. FIG. 1 illustrates the problem addressed by the present invention. In deep well applications the act of running in the tool 12 to the desired depth can create sufficient hydrostatic pressure in the control line 16 that is in excess of the setting pressure used to move the actuator associated with tool 12 so that tool 12 sets prematurely. Tool 12 can be a packer or plug or a valve or any other tool commonly used downhole in borehole 14. In depths exceeding 4000 meters this can be a serious problem and there is a need to prevent excess hydrostatic pressure from reaching the actuator for the tool 12 before the tool 12 is advanced to the desired depth in borehole 14.

FIG. 2 illustrates a string 20 extending to a tool 22 and an upper control line 24 extending to the removable barrier 26 that is in the closed position for running in. The distance between opposed arrows 28 defines the height of the fluid column in the lower control line 30. This hydrostatic pressure is chosen at a value that is lower than the pressure required to set the tool 22 with allowance for a safety factor. Thermal conditions in the well can raise the hydrostatic pressure above the tool 22. Connecting an upper completion to a lower completion that has the tool 22 can also result in reduction of tubing reference pressure seen by the actuation system for the tool 22 as the mating of a wet connect opens a tubing valve. The removable barrier 26 is preferably at least one rupture disc although several can be connected in parallel in the event an operational issue develops with one of the disc. Raising pressure from a surface location can break one or all of the rupture discs 34. While using a rupture disc is economical and simple other remotely operated valves can be used instead which respond to signals from a surface or other location delivered in a variety of ways such as pressure pulses, acoustic or an electromagnetic signal to name a few examples.

Those skilled in the art will appreciate that the present invention allows control of the hydrostatic pressure in a hydraulic control system for a downhole tool at deep setting depths that would generate enough hydrostatic pressure in the hydraulic system to set off the tool before the tool reached its desired location. The barrier in the control line strategically placed higher than the actuator for the tool to be operated such that the hydrostatic pressure in the control line stays at a lower value than the pressure that actuates the tool. Thermal effects can be taken into account by the placement of the barrier as well as drops in tubing reference pressure from connecting an upper completion to a lower completion with a wet connect.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: 

We claim:
 1. An operating assembly for a borehole tool, comprising: a hydraulically actuated tool supported on a tubular string for placement at a predetermined depth; a control line extending to an actuator for said tool, said actuator operating the tool with a predetermined pressure lower than hydrostatic pressure in said control line with said tool at said predetermined depth; a barrier in said control line that when closed limits hydrostatic pressure on said actuator to below said predetermined pressure as said tool is delivered to said predetermined depth; said barrier selectively defeated after said tool reaches said predetermined depth.
 2. The assembly of claim 1, wherein: said barrier comprises at least one rupture disc.
 3. The assembly of claim 1, wherein: said barrier is located on said control line to take thermal effects on hydrostatic pressure into account to avoid setting said tool with control line hydrostatic pressure before and when the tool reaches said predetermined depth.
 4. The assembly of claim 1, wherein: said barrier is located on said control line to take into account reduction in tubing reference pressure to said actuator from said tubing when connecting an upper assembly to a lower assembly where said tool is mounted with a wet connect.
 5. The assembly of claim 1, wherein: said tool comprises at least one of a packer, bridge plug, anchor or valve.
 6. The assembly of claim 1, wherein: said tool is located at least 4000 meters deep in said borehole.
 7. The assembly of claim 1, wherein: said barrier is broken with pressure from a surface location for the borehole.
 8. The assembly of claim 1, wherein: said barrier comprises a remotely operated valve.
 9. The assembly of claim 8, wherein: said valve is remotely operated from a surface location.
 10. The assembly of claim 9, wherein: said valve is signaled to open acoustically or with pressure pulses or with an electromagnetic field.
 11. The assembly of claim 1, wherein: said barrier is broken explosively.
 12. A method of operating a hydraulically actuated borehole tool using a control line, comprising; locating the tool at a predetermined depth where hydrostatic pressure in the control line exceeds the pressure in the control line needed for tool actuation; preventing tool actuation when moving the tool to said predetermined depth by locating a barrier in the control line to keep the hydrostatic pressure between the tool and the barrier below the needed actuation pressure for the tool; removing the barrier to actuate the tool.
 13. The method of claim 12, comprising: providing a rupture disc as said barrier.
 14. The method of claim 12, comprising: locating said barrier to allow a margin of safety with the developed hydrostatic pressure to remain below the pressure that sets the tool from thermal effects in the borehole.
 15. The method of claim 12, comprising: locating said barrier to compensate for reduction of reference pressure for an actuation system for the tool by a decrease in tubing pressure seen during engagement of a wet connect.
 16. The method of claim 12, comprising: breaking said barrier with pressure from the surface of the borehole.
 17. The method of claim 12, comprising: providing a remotely actuated valve as said barrier.
 18. The method of claim 17, comprising: actuating said valve with pressure pulses or acoustics or an electromagnetic field. 